A head mounted display (“HMD”) is a display device worn on or about the head. HMDs usually incorporate some sort of near-to-eye optical system to emit a light image within a few centimeters of the human eye. Single eye displays are referred to as monocular HMDs while dual eye displays are referred to as binocular HMDs. Some HMDs display only a computer generated image (“CGI”), while other types of HMDs are capable of superimposing CGI over a real-world view. This latter type of HMD can serve as the hardware platform for realizing augmented reality. With augmented reality, the viewer's image of the world is augmented with an overlaying CGI, also referred to as a heads-up display (“HUD”).
HMDs have numerous practical and leisure applications. Aerospace applications permit a pilot to see vital flight control information without taking their eye off the flight path. Public safety applications include tactical displays of maps and thermal imaging. Other application fields include video games, transportation, and telecommunications.
Many HMDs utilize an eyepiece that includes a lightguide to direct CGI display light from a display of the HMD to a user's eye(s). Tolerances of the lightguide may become critical to properly direct the display light, in some HMDs. If the lightguide depends on the optical phenomenon of Total Internal Reflection (“TIR”) to deliver an image to the eye of a user, the surfaces of the lightguide that facilitate the TIR must be manufactured within design parameters.